This invention pertains to apparatus for felling trees, and more particularly to such apparatus which fells trees by slicing through a tree trunk with a large blade which is opposed by, and cooperates with, an undercutting device.
In the past, devices have been built which were intended to fell trees, such devices incorporating one or more large motor-driven blades. Typically, such devices were mounted on the front end of a bulldozer or tractor. Also typical, one or more cutting blades extended outwardly from the front of a tractor, and were mounted on some type of support structure. Such blades were placed on opposing sides of a tree trunk while some type of gripping structure, also mounted on the tractor, was clamped on the trunk above blade level. The tree was then sheared off by driving the blade or blades through the trunk. Other similar devices for shearing trees were also used.
A severe problem which exists with the use of such devices is the extreme amount of shattering and crushing of wood in the trunk of a felled tree. Such devices create large shear forces in a tree during cutting. These forces cause the wood in the trunk adjacent the cut to shatter or separate. This problem renders many of the prior art devices commercially unacceptable, due to the fact that a large portion of a felled tree must be cut off before the tree can be utilized by mill operators.
A general object of the present invention is to provide an apparatus and method for felling trees which overcomes the above-stated problems in the prior art.
A preferred embodiment of the invention is mounted on the front of a tractor. A substantially planar base plate extends outwardly from the front of the tractor substantially parallel to the ground. In the base plate, a U-shaped notch, (having opposing first and second sides), suitable for receiving a tree therein, opens toward the front of the plate so that the tractor can approach a tree, and position the notch about such a tree. A substantially planar blade having a convex, arc-shaped cutting edge is pivotally attached to the base plate between the notch and the front of the tractor. In this position, the blade can be pivoted across the notch along a plane superjacent the plane of the base plate, its cutting edge sweeping from the first side of the notch toward the second side thereof. Located adjacent the second side of the notch is a pair of under-beveled surfaces. One of these under-beveled surfaces is formed in the base plate. The other is formed in an anvil which is attached to the under surface of the base plate.
Mounted on support structure for the blade, near the point at which the latter is pivotally attached to the base plate, is a nozzle for spraying lubricant, such as oil. The nozzle is directed toward the cutting surface of the blade. A pump is attached to the base plate between the blade and the front of the tractor. The pump is actuated by a rod which extends from the pump. A feed line connects the pump to the nozzle. Also, an oil supply line is connected to the pump from a source of oil on the tractor. A cam mounted on the rear edge of the blade actuates the pump each time the blade returns to its fully opened position--thus spraying oil from the nozzle onto the blade's cutting surface.
The blade is driven by an hydraulic ram. When a tree is contained within the notch, the ram is actuated, and the blade moves across the notch and through the tree at a predetermined rate of speed. In the instant embodiment of the invention, the blade moves from the first side of the notch toward the second side in approximately five seconds. When the blade begins to move, the under-beveled surfaces are driven into the side of the tree opposite the blade, undercutting the tree with respect to the blade. As the blade cuts slices through the trunk, these surfaces cause the tree to lean in the direction of blade swinging. It is the leaning of the tree with respect to blade travel speed which minimizes crushing and shattering of the fibers within a tree trunk. Too much lean with respect to blade travel speed causes excessive shattering; too little lean with respect to blade travel speed causes increased crushing.
Tests which have been performed on the instant embodiment of the invention reveal that maximum shatter occurs typically only about six inches up the trunk of a tree from the point of a cut. This is true even for frozen trees and for trees which have substantially rotten cores.
Thus, a more specific object of the invention is to provide a method and apparatus which minimizes shatter and crushing of tree fibers by undercutting the tree during slicing, and by providing a predetermined rate of blade travel speed.
Another advantage which is obtained by felling trees with the instant embodiment of the invention is that, due to the effect of undercutting a tree with respect to the blade, the tree always falls in the direction of blade cutting movement.
Thus, another object of the invention is to provide a method and apparatus for felling trees for which the direction of tree fall is predetermined.
These and other objects and advantages attained by the invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings.